System and method of two-stepped laser scattering defect inspection

Abstract

A laser scattering defect inspection system includes: a stage unit that rotates a workpiece W and transports the workpiece W in one direction; a laser light source that emits a laser beam LB toward the workpiece W mounted on the stage unit; an optical deflector that scans the laser beam LB emitted from the laser light source on the workpiece W; an optical detector that detects the laser beam LB scattered from the surface of the workpiece W; a storage unit that stores defect inspection conditions for each inspection step of a manufacturing process of the workpiece W, where the conditions include the rotation speed and the moving speed of the workpiece W by the stage unit, the scan width on the workpiece W and the scan frequency by the optical deflector; and a control unit that reads the defect inspection conditions stored for each inspection step in the storage unit and controls the driving of the stage unit and the optical deflector under the conditions.

1. A laser scattering defect inspection system that irradiates a laser beam on a surface of a workpiece to detect the light beam scattered from the surface, thereby detecting presence of defects, the laser scattering defect inspection system comprising:
 a stage mover that rotates the workpiece and transports the workpiece in one direction; 
 a laser light source that emits the laser beam that has a beam diameter toward the workpiece mounted on the stage mover; 
 an optical deflector that cross scans the laser beam emitted from the laser light source on the workpiece, where a scan width of a cross scan is a quantity of laser beam movement caused by the optical deflector; 
 an optical detector that detects the laser beam scattered from the surface of the workpiece; 
 a storage that stores defect inspection conditions for each of a plurality of inspections of the workpiece in a manufacturing process, where the conditions include a rotation speed and a moving speed of the workpiece by the stage mover, a scan width on the workpiece and a scan frequency by the optical deflector; and 
 a controller that reads the defect inspection conditions stored for each of a plurality of inspections of the workpiece in the storage and controls the driving of the stage mover and the optical deflector under the conditions, 
 wherein the controller controls the stage mover, the laser light source, the optical deflector and the optical detector, and 
 the controller performs a first inspection step of defect inspection as a preliminary inspection for performing actual condition investigation, which classifies the defects, and a second inspection step of defect inspection that only counts a quantity of the defects but does not perform actual condition investigation, which classifies the defects, 
 the optical deflector stops the cross scan when the controller performs the first inspection step, while the stage mover rotates and transports the workpiece and the optical detector detects the laser beam scattered from the surface of the workpiece, and 
 the scan width of the cross scan is controlled to be equal or larger than the beam diameter on the workpiece in the second inspection step, while the stage mover rotates and transports the workpiece and the optical detector detects the laser beam scattered from the surface of the workpiece. 
 
     
     
       2. The laser scattering defect inspection system according to  claim 1 , wherein:
 the optical deflector is an acousto-optical deflector which comprises an acousto-optical medium and a piezoelectric vibrator capable of causing an ultrasonic wave to propagate through the acousto-optical medium; and, 
 the controller controls the scan width on the workpiece and the scan frequency by the optical deflector by controlling the vibration conditions of the piezo-electric vibrator. 
 
     
     
       3. A laser scattering defect inspection method for detecting defects, comprising:
 providing a complex scan combining a spiral scan that scans a laser beam with a beam diameter on a workpiece in a spiral form by rotating and transporting the workpiece in one direction and a cross scan that deflects the laser beam using an optical deflector to be scanned on the workpiece, where a scan width of the cross scan is a quantity of laser beam movement caused by the optical deflector; 
 scanning a surface of the workpiece to detect laser beams scattered from the surface of the workpiece; 
 a first inspection step of performing defect inspection as a preliminary inspection for performing actual condition investigation, which classifies the defects; and 
 a second inspection step of performing defect inspection that only counts a quantity of the defects but does not perform actual condition investigation, which classifies the defects, wherein: 
 the cross scan of the optical deflector is stopped in the first inspection step, while the workpiece is rotated and transported and the laser beam scattered from the surface of the workpiece is detected; and 
 the scan width of the cross scan is controlled to be equal or larger than the beam diameter on the workpiece in the second inspection step, while the workpiece is rotated and transported and the laser beam scattered from the surface of the workpiece is detected. 
 
     
     
       4. The laser scattering defect inspection method according to  claim 3 , wherein the first inspection step is performed while the beam diameter on the workpiece is equal to or larger than 0.5 μm and equal to or smaller than 25 μm. 
     
     
       5. The laser scattering defect inspection method according to  claim 3 , wherein the second inspection step is performed while the beam diameter on the workpiece is equal to or larger than 0.5 μm and equal to or smaller than 25 μm, the scan width of the cross scan is equal to or larger than the beam diameter and equal to or smaller than 5 mm, and a scan frequency of the cross scan is equal to or higher than 10 MHz and equal to or lower than 1,000 MHz. 
     
     
       6. The laser scattering defect inspection method according to  claim 4 , wherein the second inspection step is performed while the beam diameter on the workpiece is equal to or larger than 0.5 μm and equal to or smaller than 25 μm, the scan width of the cross scan is equal to or larger than the beam diameter and equal to or smaller than 5 mm, and the scan frequency of the cross scan is equal to or higher than 10 MHz and equal to or lower than 1,000 MHz.